http://en.wikipedia.org/wiki/Teen_Buzz
If the speaker can produce 17.4kHz then it could be sufficiently
annoying to any potential 'teenage hooligan' running off with your
phone.
Add in some remote-access features, such as lock-down, sync/wipe local
data, gps/voice recording+uploading.. if everything worked together,
you could get enough info, then print a message on the screen:
"Thank you for borrowing my phone, there is a McDonalds approx 100m
north of your current location.. leave it on a table there and I will
not prosecute. Your voice and locations have been recorded and
uploaded to the internet (see map of your travels below). This means
that destroying this phone, although fun, will not make it harder to
identify you. [i agree] [i disagree]"
Upon choosing the latter option, the poor thief would be berated by
whatever messages you like through the speaker:
* I think the Government is Hip!
* Help! I'm being stolen by a silly person!
* I wish to be stolen by someone less inept!
etc, etc
I guess the first stage of lockdown would be cutting off all private
data access, whilst tracking and recording take place.. so that any
outgoing calls could also be monitored and recorded. It would be very
nice to do this monitoring from a web-interface too..
Richard